This invention relates to the field of apparatus for performing polymerase chain reaction ("PCR") and, more particularly, to a tool for removing and installing caps of PCR reaction tubes.
PCR is a widely used procedure in which a small amount of DNA is amplified (i.e., reproduced) to yield a higher concentration of the DNA for further study, testing, etc. See U.S. Pat. No. 4,683,195 and U.S. Pat. No. 4,683,202. The steps of the reaction require the samples to undergo a series of thermal treatments wherein the samples are repeatedly cycled between two temperatures, such as between 70.degree. C. and 94.degree. C. about 35 times. It has become common to perform PCR in reaction tubes. The reaction tubes are small plastic containers (each holding approximately 0.2 ml) having a generally cylindrical shape with a conical bottom and a removable cap at the top. Because of their small size, the tubes are commonly sold connected together in strips of 8 or 12 tubes. An equal number of caps is provided as a matching strip. A strip of caps has tabs at each end to facilitate removal of the strip.
Twelve strips of 8 tubes ordinarily are loaded into wells in a tube rack for processing. In some apparatus, four such tube racks are processed simultaneously. In use, the operator loads a strip of capped tubes into the tube rack and removes the strip of caps by pulling on the tab to lift the caps progressively from one end to the other. The tubes are then loaded with the appropriate reagents, usually with a micro-pipette and recapped by hand. The procedure of uncapping and recapping is repeated after the PCR process to remove the samples for analysis.
If the tubes are empty, the act of removing the strip of caps in rapid succession obviously does not present any problem of ejecting the contents. However, when necessary to uncap the tubes when they are full or partially full (as in the case of tubes purchased pre-packaged with reagents), it is often the case that some of the contents will be released. It is even sometimes the case that recapping the tubes might result in spillage of some of the contents. To minimize spillage, the technician will typically need to carefully remove and/or replace one cap at a time, which is not only tedious and time consuming, but also requires repetitive movements. Also, spillage of DNA material is highly undesirable because of the potential for contamination of adjacent and subsequent reactions. Moreover, practice has shown that the closely packed tubes in the tube rack are difficult to recap. A careless or hurried technician may not always get all tubes properly recapped all of the time which can result in test failures due to evaporation during heating. Even when the tubes are uncapped while empty, removing strips of caps by hand often results in stretching of the strip making recapping difficult and subject to failure.